A geostationary orbit, geostationary Earth orbit or geosynchronous equatorial orbit (GEO) is a circular orbit 35,786 kilometres above the Earth's equator and following the direction of the Earth's rotation. These are the orbits in which time period of orbital motion of satellite is equal to the time period of spin motion of Earth about its axis. An object in such an orbit has an orbital period equal to the Earth's rotational period (one sidereal day) and thus appears motionless, at a fixed position in the sky, to ground observers. Satellites placed in geostationary orbits allow the communication with satellite antennas (located on Earth) without have to rotate to track them, but can be pointed permanently at the position in the sky where the satellites are located.

H2020

Horizon 2020 (H2020) is the European Framework Programme for Research and Innovation. H2020 is the biggest EU Research and Innovation programme ever with nearly €80 billion of funding available over 7 years (2014 to 2020). Horizon 2020 is open to everyone, with a simple structure that reduces red tape and time so participants can focus on what is really important. This approach makes sure new projects get off the ground quickly – and achieve results faster.

HET

Hall Effect Thruster.

Isp

Specific impulse (usually abbreviated Isp) is a measure of the efficiency of rocket and jet engines. By definition, it is the total impulse (or change in momentum) delivered per unit of propellant consumed and is dimensionally equivalent to the generated thrust divided by the propellant mass or weight flow rate. If mass (kilogram or slug) is used as the unit of propellant, then specific impulse has units of velocity. If weight (newton or pound) is used instead, then specific impulse has units of time (seconds). Multiplying flow rate by the standard gravity (g0) converts specific impulse from the mass basis to the weight basis.

LEO

A low Earth orbit (LEO) is an orbit around Earth with an altitude of 2,000 kilometers or less, and an orbital period of between about 84 and 127 minutes. Almost all human spaceflights have taken place in LEO or below.

MEO

A medium Earth orbit (MEO) is the region of space around the Earth above low Earth orbit (altitude of 2,000 km) and below geostationary orbit (altitude of 35,786 km).

PSA

Programme Support Action

SRC

Strategic Research Cluster

The CHEOPS project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 730135.